In drywall construction, gypsum wallboards are affixed to vertical studs and horizontal joists to form the walls and ceilings of a room. Joint compounds are used to conceal the joints between adjacent boards and at corners. A paper joint tape is commonly used along with the joint compound to provide a bridging strength to the joint compound, when the compound dries or sets.
When applying joint compounds at inside corners, the compound, in a relatively stiff aqueous slurry form, is spread with a broad knife along a first wall adjacent the inside corner and then, after this had dried or set to a substantial degree, applying more of the same compound, relatively stiff aqueous slurry form, to the other, second wall adjacent the same corner.
A problem arises in applying the joint compound to the second wall if there happens to be a gap, between the two wallboards forming the inside corner, which the broad knife can slip into, as the compound is being applied with the knife. This problem is particularly aggravated if a paper tape is being used, as is most commonly the case.
It is very easy for the knife to be urged too tightly into the corner in applying joint compound to the second wall, moving, moving into the gap, mentioned above, creating a groove into the joint compound which had dried or set on the first wall. If joint tape is being used, this occurs as the tape is being bedded with compound, and the center portion of the tape is pushed into the gap.